Browsing by Author "Penttala, Vesa, Professor emeritus, Aalto University, Department of Civil and Structural Engineering, Finland"

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    A novel application of mineral powders in normal strength concrete
    (Aalto University, 2013) Tikkanen, Johanna; Rakennustekniikan laitos; Department of Civil and Structural Engineering; Insinööritieteiden korkeakoulu; School of Engineering; Penttala, Vesa, Professor emeritus, Aalto University, Department of Civil and Structural Engineering, Finland
    The possibility of using inert mineral powders to replace a part of the cement in concrete and the effects of replacement on the properties of fresh and hardened concrete were studied. In the past, studies of the influence of fillers in concrete have mainly been focused on high strength, self-compacting and high-performance concretes. However, in the current research,the focus was on normal-strength concretes, with adequate to good consistency. According to the results, mineral powders had a considerable effect on the properties of the cement paste and concrete. The results obtained show that mineral powders can replace cement to a moderate extent, mainly as the result of the reduced water demand of the mineral powder concretes. In concretes with the same amount of cement and similar consistency,mineral powder concretes obtained higher strengths as a result of their lower amount of water.The use of mineral powders had a greater effect on the water demand of concrete than directly on the compressive strength. The direct strength gain, presumably caused by chemical activation of the hydration of cement via heterogeneous nucleation, was, on average, from 0 to5 MPa. Finally, a statistical model, based on over 70 mix compositions, is proposed for the quantification of the effects of the addition of the powder on the flow and compressive strength of the concrete.The use of mineral powders in itself was not observed to affect the freeze-thaw resistance,but the consequent binder reduction and strength loss reduced the freeze-thaw resistance.However, it is concluded that the strength loss resulting from the replacement of the cement could be compensated for by reducing the w/c ratio of the mineral powder concretes because of the lowered water requirement. The use of mineral powders also had an effect on the hydration and microstructure of the concretes. The maturities of the concretes containing mineral additions were continuously higher than that of the reference. In addition, a moderate cement reduction was not observed to have detrimental effects on the microstructure of the concrete. This work suggests that part of the cement can be replaced by inert powders, which lower the water demand of the concrete and thus allow a partial cement reduction. The advantages of the use of mineral powder in concrete include lower CO2 emissions and energy consumption in cement and concrete production and the potential to improve the cost-effectiveness of concrete manufacturing.